The present invention relates to a new and improved construction of an ion-sensitive capillary electrode containing an electrode housing in which there is formed a bore and in which there is located a membrane electrode, and further, the invention relates to a new and improved method for the fabrication of such ion-sensitive capillary electrode.
There are known to the art specific ion-selective electrodes for a large number of single or multi-valent ions. They are classified in accordance with the physical condition of the substance which forms the electrode membrane. Consequently, there are known two large groups of ion-selective electrodes:
(1) Ion-selective electrodes having a solid membrane or diaphragm. Such type electrodes can possess either a homogeneous membrane (single crystal, crystalline substance or glass) or an heterogeneous membrane, where a crystalline substance in incorporated in a matrix formed for instance of a polymer. PA1 (2) Ion-selective electrodes with liquid membranes.
In this case the membrane of the electrodes consists of a liquid which is immiscible with water, in which there is dissolved a substance which together with the ion in the solution, for which the electrode is selective, forms an associate or can exchange such.
Such type electrode generally consists of a cylindrical shaft formed of polymeric material at the tip of which there is secured a membrane of the above-mentioned type. The hollow cylindrical shaft contains auxiliary means for producing an electrical contact between the side of the membrane which confronts the interior of the shaft and an electrical leak or shunt conductance. A frequently employed embodiment of such type contact arrangement resides in that an electrolytic solution of suitable composition establishes both the contact with the membrane and also with a conductance electrode (as a rule of the type silver-silver chloride). The conductance electrode can be connected by means of a connection cable with the input of a high ohm amplifier at which there is also connected a standard reference electrode. For measurement purposes the specific ion-sensitive electrode and the reference electrode conjointly immerse in the solution to be examined. The electrical potential difference between the selective ion-sensitive electrode and the reference electrode is a measure for the activity of the ions in the solution and which are to be measured. An embodiment of such type shaft-like specific ion-sensitive electrode has been disclosed for instance in the German Patent Publication No. 2,021,318.
Such type shaft-like selective ion-sensitive electrodes are completely suitable for a large number of fields of application. For the analysis of microsamples having a volume of a few microliters such type electrode however cannot usually be employed, since miniaturization thereof is associated with technological difficulties. Therefore, there have been proposed to the art selective ion-sensitive electrodes wherein the active membrane is present in the form of a capillary or as part of a capillary. Capillary-shaped electrodes, wherein part of the capillary is formed by a liquid membrane, have been disclosed by H. F. Osswald in the publication Chemia, Volume 31, 1977, Nr. 2. It has been found that such type capillary-shaped electrodes exhibit large advantages from the measurement standpoint.
The heretofore known constructional embodiments are however associated with the drawback that a number of electrodes must be mutually connected in a row either by hose sections or prefabricated plastic fitting elements. As a result the exchangeability of the electrodes and the cleaning and drying of the capillaries, following a measurement operation, is rendered more difficult.